Upper and lower fatigue life limits model using energy-based fatigue properties

Abstract Cyclic strain-life data and corresponding Coffin-Manson coefficients for both normal and shear strain-lives were first defined. Energy-fatigue life curves were then generated from strain-fatigue life properties. The upper and lower limits of life are estimated using the proposed life equations. The upper life limit is obtained by assuming that the dominant cracking mechanism is Case A and the lower life limit is obtained by assuming that the dominant cracking mechanism is Case B. The proposed method was developed based on physical evidences of crack initiation and growth as well as the amount of dissipated energy over life cycles. The fatigue life data fall between the upper and the lower limits resulting in a promising life prediction. The proposed method has been used to evaluate the fatigue life of various metallic materials of SAE 1045, AISI 304, Inc 718 and Haynes 188 reported in the literature. Results of fatigue life predictions were found in good agreement with experimental life data.

Effects of a Staff Development Program on Head Nurses' Communication Skills and Job Satisfaction

Background: Communication skills of operational managers such as head nurses greatly influence the performance of nursing personnel and by extension, the quality of the care provided by them. Objectives: This study was conducted to identify the role of a development program on communication skills and job satisfaction in head nurses. Materials and Methods: This research was a non-randomized two-group trial. A random allocation of two hospitals affiliated to Tehran University of Medical Sciences created an intervention and control group. In the intervention group, all head nurses were entered in a two-day communication skills development workshop using adult learning theory. The head nurses of the other hospital were allocated to the control group. Job satisfaction and communication skills of head nurses were investigated prior and 6 weeks following intervention in two groups. The data were analyzed by Chi-square, Fisher exact test, T-test, paired t test and analysis of covariance. Results: Following intervention, the communication skills scores achieved by intervention group were 127.5 ± 7.10 at pretest and increased to 134.11 ± 7.32 after the intervention (P < 0.01). The mean score of the communication skills did not alter significantly in the control group. Moreover, no significant change was observed in the mean scores of job satisfaction of head nurses in the intervention group compared to those of the control group (P = 0.102). Conclusions: The development programs of communication skills resulted in an increased level of communication skills in the head nurses. However, more effective steps have to be taken in professional and organization conditions to enhance head nurses’ job satisfaction level. Keywords: Job Satisfaction; Communication; Nursing, Supervisory; Growth and Developmen

Local Ratcheting at the Notch Region of Non-Press-Fitted and Press-Fitted Al 7075-T6 Samples Undergoing Asymmetric Stress Cycles

The present study evaluated the ratcheting response of notched and press-fitted Al 7075-T6 specimens under stress-controlled asymmetric cycles. The degree of the interference fit (DIF) directly influenced the magnitude and the rate of progressive plastic strain at the notch edge region. Local ratcheting at the hole–pin interference region was analyzed by means of two kinematic-hardening rules—the Ahmadzadeh–Varvani (A–V) rule and the Chaboche rule—coupled with the Neuber rule. Ratcheting strains at the notch root of aluminum samples with DIF = 0 (non-press-fitting samples) were measured and found to be the highest in magnitude. For the press-fitted samples, however, ratcheting strains dropped noticeably as the DIF increased from 1% to 2%. The press-fitting process plastically deformed the perimeter edges of the notches and improved the materials strength locally at the notch edges, resulting in better resistance against ratcheting progress. Local ratcheting strains at distances of 0.5, 1.3, and 3.0 mm from the notch roots were predicted for both pinned and unpinned samples via the hardening rules and were compared with those of measured ratcheting values. The ratcheting curves predicted by means of the A-V and Chaboche hardening rules closely agreed with the experimental data. The predicted ratcheting curves were positioned, respectively, above and below the measured ratcheting data

Ratcheting–Fatigue Damage Assessment of Additively Manufactured SS304L and AlSi10Mg Samples under Asymmetric Stress Cycles

The present study aims to investigate the interaction of ratcheting and fatigue phenomena for additively manufactured (AM) samples of SS304L and AlSi10Mg undergoing uniaxial asymmetric stress cycles. Overall damage was accumulated through fatigue and ratcheting on AM samples prepared from three-dimensional-printed plates along vertical and horizontal directions. Fatigue damage was evaluated based on the strain energy density fatigue approach and ratcheting damage was calculated through use of an isotropic–kinematic hardening framework. The isotropic description through the Lee–Zavrel (L–Z) model formed the initial and concentric expansion of yield surfaces while the Ahmadzadeh–Varvani (A–V) kinematic hardening rule translated yield surfaces into the deviatoric stress space. Ratcheting of AM samples was simulated using finite element analysis through use of triangular and quadrilateral elements. Ratcheting values of the AM samples were simulated on the basis of Chaboche’s materials model. The predicted and simulated ratcheting damage curves placed above the experimental fatigue–ratcheting experimental data while predicted fatigue damage curves collapsed below the measured values. The overall damage was formulated to partition damage weights due to fatigue and ratcheting phenomena